Patent Application
20100051545
The invention relates to membrane filtration modules having one or more hollow permeable membranes mounted therein and more particularly to protection for such membrane modules.
During the membrane filtration process, foreign particles/materials contained in the feed approach the membrane surface and are caught in the membrane module. Those particles cause membrane fouling and can clog membrane modules. Liquid backwash, air scouring and chemical cleaning are common means to remove the fouled materials. However, the membrane modules still often suffer from packing by fibrous materials or damage by sharp materials or objects. Typically fibrous materials or trash may be caught around membranes and inside the membrane groups or bundles when wastewater or mixed liquor from a biological system is filtered. Another example is the seawater pre-treatment with membrane filtration where sharp shells from sea water often cause damage to membranes.
Different methods have been proposed to protect the membrane modules from damage by foreign materials and objects. Pre-screen of feed is a common method to protect membrane modules from damage by large size materials. In membrane bioreactors, a screen with perforated mesh is inserted between the biological tank and the membrane tank to protect the membranes and modules. In this arrangement, a large screen has to be used and special aerators need to be installed to clean the screen.
One known method of protecting membranes includes holding a bundle of capillaries together with an open sleeve or casing. The coarse materials, like hair, are filtered by the sleeve so that these materials can not intrude into the inner section of the membrane bundle. However, the method neglects a fact that the materials smaller than the openings can pass through the open sleeve, move towards the membrane surface and inner fibre bundles, and agglomerate around and inside the fibre bundles. It is difficult for these materials to be removed out of the open sleeve. Gradually these materials accumulate inside the membrane bundle and on the inner surface of the sleeve and the bundles eventually become packed with these materials.
It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.
According to one aspect, the present invention provides a filtration system for removing fine solids from a liquid suspension comprising:
a vessel for containing said liquid suspension;
one or more permeable, membranes within the vessel;
means for providing a pressure differential across walls of said membranes such that some of the liquid suspension passes through the walls of the membranes to be drawn off as permeate;
a screen positioned in a flow path of the liquid suspension through to said membrane walls; and
means for withdrawing permeate from the membranes.
According to another aspect, the present invention provides a filtration system comprising:
a membrane module comprising a plurality of permeable membranes, each of the membranes having a first end and a second end, the membranes having one of said ends extending from and mounted to at least one potting head, and a screen surrounding the membranes.
According to another aspect, the present invention provides a filtration system comprising:
a membrane module comprising a plurality of permeable membranes, each of the membranes having a first end and a second end, the membranes having one of said ends extending from and mounted to at least one potting head, said module having an upper and a lower end;
a screen surrounding the membranes and extending between said upper and lower ends of said module; and
an opening being provided in said screen at or adjacent said upper end of the module.
In one embodiment, said opening is provided by peripherally spacing an end of said screen from said upper end of the module. In another embodiment, said opening is provided by extending said screen to below said upper end of the module. Preferably, the upper end of said module comprises said at least one potting head.
Preferably said screen is a fine screen. For preference, the aperture size of the screen is between about 625 μm2 to about 25×106 μm2 and more preferably, between about 1×104 μm2 to about 1×106 μm2.
Preferably, the screen is connected to and extends from said potting head.
In one form of the invention, the membranes are sealed at the first end and open at the second end to allow removal of a filtrate, though it will be appreciated that in some forms of the invention the membranes are open at both ends to allow filtrate removal from both ends. Preferably the membranes comprise hollow fibre membranes. For preference, the fibres are arranged in close proximity to one another and mounted in a bundle in a substantially taut manner between an upper potting head and a lower potting head to prevent excessive movement therebetween. Preferably, the fibres are substantially uniformly mounted in the lower potting head relative to a distributed array of aeration holes in the lower potting head, wherein the aeration holes are sized and located such that bubbles, formed by a pressurized gas passing therethrough when the module is immersed in a liquid, pass substantially uniformly between the fibres.
For preference the vessel includes a plenum chamber beneath the lower potting head through which the pressurized gas is introduced, and wherein the plenum chamber includes an aperture substantially beneath the aeration holes for allowing egress of contaminants.
For preference, the lower potting head is connected to a source of the pressurized gas, and the fibres and screen are arranged to be vibrated by the gas bubbles.
According to another aspect, the present invention provides a membrane module, comprising a plurality of permeable membranes,
said membranes being arranged in close proximity to one another to form an array,
the module having a header in which one end of each of the membranes is mounted, and
a screen surrounding said array of membranes.
For preference, the screen extends from said header. Preferably, the screen is connected to the header. Preferably, said screen is a fine screen. For preference, the aperture size of the screen is between about 625 μm2 to about 4×106 μm2 and more preferably, between about 1×104 μm2 to about 1×106 μm2.
Preferably, the header is connected to a source of pressurized gas so as to permit formation of gas bubbles such that, in use, the bubbles move past the surfaces of and vibrate said membranes and said screen to dislodge fouling materials therefrom.
For preference, the porous membranes comprise hollow fibre membranes. Preferably, the fibre membranes are arranged in bundles surrounded by the screen.
According to another aspect, the present invention provides a method for filtering a feed liquid, the method comprising:
providing a vessel;
providing a membrane module, the membrane module comprising:
providing a feed liquid to the vessel;
applying a transmembrane pressure to the membranes in the module, whereby a filtrate passes through pores in the membranes, thereby producing a concentrated feed comprising a fouling material in the vessel; and
removing the fouling material from the vessel.
Preferably, the membranes are mounted in a header in close proximity to one another so as to prevent excessive movement therebetween. For preference, the membranes form an array.
Some module arrangements have holes in the lower potting head for providing feed liquid to the membranes that may bypass a screen provided around the membranes. Although the low pressure drop across the screen due to its larger surface area means that most of the feed flow will still be screened, an additional screen can be fitted across the holes below the module, if required.
In one embodiment, the feed liquid is provided, at least in part, through a port in said module and fouling material is withdrawn through said port, said port having a selectively operable screen arranged such that feed flowing into said module is screened and fouling material flowing from said module is not screened.
By adding a fine mesh to the membrane module it is possible to provide a screen surface, which can provide a relatively large screen at a modest cost, without the need for external capital equipment. In the case of a membrane arrangements using aeration scouring to clean the membranes within the module, the aeration process normally used to clean the module, may also vibrate the screen, and dislodge any material therefrom that has accumulated. Dislodged material leaves the system through the normal drain-down process. So in addition to a backwashable screen, there is no need for a separate screens handling system as required in the prior art.
It will be appreciated by those skilled in the art that the present invention may be used with pressurised modules, membrane bioreactor modules, submerged modules or any variations thereof. The invention may also be applied to racks of modules rather than to the separate modules that make up the rack, by enclosing the rack of modules in the screen material.
Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:
Referring to
In use, the module 4 is arranged vertically in a feed tank (not shown). During filtration the filtrate is withdrawn from the top potting head 6 and filtrate collection chamber 11 through suction applied to the open ends of the membrane lumens. The suction produces a pressure differential across the membrane walls resulting in feed liquid being drawn from the feed tank through the screen 8 and into contact with the hollow fibre membranes 9. The screen 8 has apertures dimensioned to remove coarse contaminant matter within the feed liquid prior to its application to the membranes.
Although this embodiment suffers some decrease in effectiveness due to the ingress of course contaminant matter through the aperture 50 (which is not protected by screen 8), this is generally balanced from a performance/practical perspective by advantages stemming from the free flow of concentrate and waste (including course contaminant matter) outwardly through aperture 50, typically during the backwash process.
Gas, typically air, is introduced into the bottom of the module 4 through holes 10, producing gas bubbles between fibres to scrub solids accumulated on membrane surfaces. The gas bubbles also result in vibrating and scouring of the screen 8 to remove accumulated screening therefrom. When the feed tank is drained following a backwash, the screenings dislodged from the screen 8 are also removed.
The gas bubble cleaning process and method may be used in conjunction with any standard backwashing regimes including liquid backwashing, pressurised gas backwashing, combinations of both, as well as with chemical cleaning and dosing arrangements.
The gas bubble cleaning process would normally be used in conjunction with the backwash stage, however, it may also be used continually during the filtration and backwash stages. Cleaning chemicals such as chlorine may be added to the gas providing the bubbles to further assist the cleaning process. Solids removed in the cleaning process may be intermittently or continually removed.
Screen aperture dimensions are chosen to reject debris entering the membrane module, but allow gas to escape during the gas bubble cleaning process. For finer screens a gas vent can be provided instead of relying on the gas passing out through the screen. The screen can be formed of self-supported hard material or a flexible material that allows swaying of the screen during the gas-bubbling cleaning process.
It will be appreciated that further embodiments and exemplifications of the invention are possible without departing from the spirit or scope of the invention described.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007901821 | Apr 2007 | AU | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/AU08/00491 | 4/4/2008 | WO | 00 | 10/2/2009 |
